A master cylinder for controlling a brake system is known, for example, from DE 10 2004 057 137 A1, which is incorporated by reference, the control passages being provided as radial transverse bores of small cross section and a circumferential internal groove being formed on an inner side in the region of the transverse bores in order to keep the dead travel of the master cylinder as short as possible and at the same time to lower the throttling resistance by reducing the length of the transverse bores.
With the use of a controlled brake system such as a brake system with traction control (ASR) or electronic stability program (ESP), in the event of a control intervention pressure medium is fed by a pump from a pressure medium reservoir via the master cylinder. A disadvantage here is that the small cross section of the transverse bores generates excessive flow resistance and the required pressure medium cannot be made available to the pump quickly enough.
In order to reduce the flow resistance, there is with the known master cylinders the possibility of providing a larger number of transverse bores or of optimizing the transverse bores with respect to their diameter. However, a disadvantage of the first-mentioned solution emerges in that the flow resistance is reduced to the benefit of the stability of the piston and, moreover, the provision of a large number of small transverse bores is uneconomic. The second solution has the disadvantage that the dead travel of the master cylinder is increased by displacement of the controlling side edge of the bores.
To avoid these disadvantages, DE 10 2009 054 695 A1, which incorporated by reference, proposes that the piston is made of plastics material and the control passages of the piston have a control edge formed parallel to an end face of the piston, the control passages being configured as axial grooves on an outer side of the piston. This makes it possible to increase the flow cross section of the control passages while the closing travel remains the same, so that dynamic behavior during control interventions can be improved. The axial grooves have the advantage that defined guidance of the sealing element on the outer side of the piston is ensured.